When an earthquake or other disaster strikes, nuclear-power plants are designed to go into automatic shutdown. But the nuclear fuel in the reactors still needs a continual supply of cooling water, as does the "spent," or used, fuel that is stored in large pools. And they need power to move that water.

Nuclear-power plants across America, including Palo Verde, already have exhaustive emergency precautions in case they lose power. But despite confidence in Palo Verde's ability to withstand natural disasters or terrorist attacks, the specially assembled response team is reviewing the best options in the highly unlikely event that every available power source at the plant is damaged.

They review the backup systems that will kick in. Then, they consider what would happen if those systems failed, as they did at Japan's Fukushima Dai-ichi power plant.

The backup-power systems for Palo Verde, just 50 miles west of downtown Phoenix, are extensive.

If power was lost, emergency diesel generators would fire up at each reactor. If the generators didn't work - as happened in Japan - they each would have their own backup generator, with seven days' worth of fuel.

Each reactor also has sets of batteries designed to run the plant for several hours. Plant officials said that by shutting off non-essential equipment, they could stretch the batteries out for three days. However, the batteries are not powerful enough to run the large water pumps for the reactors.

The last line of on-site defense at Palo Verde is two natural-gas-fired generators. They have enough stored fuel to run one generator for four to six days or both generators for two to three days.

Plant officials believe the fallback system is extensive enough to protect the nuclear fuel in any type of natural disaster, fire or terrorist attack they have foreseen.

Now, in what has been dubbed the "Japan Room," planners are trying to figure out what they haven't foreseen.

Deprived of all power, could they call on nearby Luke Air Force Base to fly in a backup generator using a heavy-lift helicopter?

Would local fire departments have enough pumper trucks to spray water on the hot reactors, as they did in Japan?

Could they string a new power line to one of the nearby natural-gas-burning power plants in time to stop a disaster?

"Part of what we are looking at is: OK, we don't know how you would get in this situation," said Bob Bement, senior vice president of operations at the plant. "But, if you did, how would you handle it?"

Worst-case review

The team has been assembled by Arizona Public Service Co., which runs Palo Verde and is the largest of the seven owners of the plant.

The experts will be assigned to the Japan Room for several months, Bement said.

The room is lined with maps and flow charts. Some show safety reviews for different departments. Others show suggested safety measures.

Along one wall is a table stacked with dozens of technical papers, including some from nuclear-watchdog groups that frequently criticize the industry.

At the head of the Japan Room is engineer Mike Powell, director of nuclear-fuel management.

"We had to check our readiness were something to happen," Powell said. "We want to learn: What can we do to make the industry better, and what can we do to make ourselves better."

The industry conducted a similar worst-case review of its safety precautions after the terrorist attacks of 9/11, which ushered in stricter safety standards, Bement said.

The Japanese event gives the industry another opportunity to ensure its safety measures are robust enough to prevent disasters, he said.

The largest concern is losing off-site electricity.

When Palo Verde's reactors are shut down for refueling, which happens every 18 months, 378,000 gallons of water submerge the core more than 24 feet underwater while the operators swap out the fuel.

Unlike most nuclear facilities in the world, Palo Verde is not near a major river, ocean or other body of water. But with 13 to 17 days' worth of water stored on-site, power to move water is a more vital concern than water itself, officials said.

Palo Verde officials believe the Japanese tsunami flooded the area at the plant where new off-site power lines could have been connected, Bement said. Unlike the Japanese plant, the emergency systems at Palo Verde are all separated and less likely to be taken out in a single event, he said.

Another difference at Palo Verde, besides the design of the reactors and the safety equipment, is the pools where spent fuel is kept.

In Japan, those pools were 140 feet off the ground in the same building as the reactors. Spent radioactive fuel needs to be kept underwater, but without power some of the Japanese plant's rods overheated and released radiation into the atmosphere.

At Palo Verde, the spent fuel is about 40 feet high and kept in an adjacent, hardened building, where it would be much easier to keep cool because water wouldn't have to be pumped so high, assuming the plant had a power source.

With no other options, Japan's plant operators relied on firefighting pumper trucks and helicopters dumping water on the reactors and spent-fuel pools.

Still, in a similar worst-case scenario, Palo Verde officials want to know where they could turn.

On one wall in the new emergency room is a map of every military base, power plant or other industrial facility within several hundred miles.

Powell and his group are contacting each one to determine what generators or other equipment they have that could help the power plant in the event of a catastrophe, and whether they have heavy-lift helicopters that could deliver it fast.

They also are gathering information on every nearby firefighting department.

"We are leading some of the short-term and long-term corrective actions for the industry here," Powell said. "We are determining what we can do as an industry to react and plan."

The control-room operators at Palo Verde practice tasks in simulators so they know how to handle problems when they arise.

They don't routinely practice putting the plant into a "meltdown"; but, every six years, the operators must rehearse their emergency procedures in the event the plant releases a radioactive plume. The latest test was conducted just days before the Japanese earthquake.

If radiation were released from Palo Verde, the Departments of Defense or Energy would conduct routine flights over the plant to take radiation readings and map the plume of radiation to help direct evacuation orders, if they were needed, Bement said.

Mobile teams also would be sent into the desert around the plant to measure radiation and coordinate evacuations.

NRC task force

The government's Nuclear Regulatory Commission has appointed a task force to review U.S. plant procedures in light of the Japanese event.

The U.S. has 104 nuclear reactors at 65 sites, run by 26 companies.

"While we are confident about the safety of U.S. nuclear-power plants, our regulatory agency has a responsibility to the American people to undertake a systematic and methodical review of the safety," NRC Chairman Gregory Jaczko said in a recent speech. "Examining all of the available information is an essential part of that effort."

At Palo Verde, Bement said, the Japanese event shows that current reactor designs used in Japan and the U.S. are robust because they survived the earthquake and the tsunami, although the issue of backup power is now key.

Preventing accidents, he said, is important not just for the area around a plant but for the image of the whole industry.

"Japan will show that, even in the worst event, today's reactors will be fine," Bement said. "The psychological harm will be worse than the radiological damage."